Amanitin binding proteins

RNA polymerase II transcribes messenger RNA and a few other small cellular RNAs. Class II promoters are usually defined by their sensitivity to a-amanitin. Like prokaryotic promoters, many class II promoters contain two conserved sequences, called the CAAT and TATA boxes. The TATA box is bound by a specialized transcription factor called TBP (for TATA-Binding-Factor). Binding of TBP is required for transcription, but other proteins are required to bind to the upstream (and potentially downstream) sequences that are specific to each gene. Like prokaryotic transcripts, eukaryotic RNAs are initiated with a nucleoside triphosphate. Termination of eukaryotic mRNA transcription is less well understood than is termination of prokaryotic transcription, because the 3 ends of eukaryotic mRNAs are derived by processing. See Figure 12-9. 

For all contact sites that could be identified, the method used in this study allowed calculation of the strength of the interactions expressed in AAG° values. In this respect, the method is complementary to X-ray analysis, which gives the exact distance, but no values for binding energies. Work is in progress to characterize such amanitin protein complexes also by X-ray analysis. From one of the monoclonal antibodies the Fab fragment was prepared and crystallized in the presence and the absence of amanitin. The structure of the complex waits to be elucidated. 

Baumann, K.H., Zanotti,G., and Fauistich, H., 1994, A P-tum in a-amanitin is the most important structural feature for binding to RNA polymerase II and three monoclonal antibodies. Protein Science 3 750-756... 

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